Update — solved! The issue was the FCM message format, not the token/key/config. A data-only FCM message is never displayed by iOS when the app is killed. I confirmed this by sending a direct FCM v1 message to the device token with a notification block + an apns override (apns.payload.aps.alert) — it displays perfectly. So the FCM token, APNs Auth Key, Firebase config and capability were all correct the whole time. The fix was simply to include a notification / apns payload instead of sending data-only. Thanks for the tip to check the FCM response — the HTTP 200 (no THIRD_PARTY_AUTH_ERROR / UNREGISTERED) is exactly what confirmed the delivery path was fine and isolated it to the payload. Posting the resolution in case it helps others. 🙏

Thanks for the reply — by "checks" I just meant the standard troubleshooting/verification steps 🙂 Environment: iPhone: iOS 26.5 Xcode 26.5 (17F42), macOS 26.5.1 Flutter 3.44.2 — the app uses firebase_messaging for push. Core issue: a direct FCM test message (Firebase Console → "Send test message") to a valid registration token from the device delivers nothing (app killed, lock screen, notification permission fully ON). Verified correct: TestFlight build with aps-environment=production; GoogleService-Info.plist matches the Firebase iOS app (project la-french, sender 649219813428); valid FCM token; APNs Auth Key in Firebase with correct Key ID + Team ID — tried two keys (one Production, one Sandbox & Production), neither delivers. Bundle com.thomasmanfredini.lafrench, Team 7TWV3839F3. Since even a direct FCM test fails with a valid token and correct config, what could prevent APNs from delivering to this app/account? What should I check next? Many thanks for your support> Thomas